Measurement of IgD by a Double Antibody Radioimmunoassay: Demonstration of an Apparent Trimodal Distribution of IgD Levels in Normal Human Sera

Abstract

A double antibody radioimmunoassay (RIA) was developed to measure IgD in serum and secretions. One IgD myeloma protein was used as radiolabeled antigen and standard with antiserum to a second IgD myeloma protein. The IgD standard and normal sera yielded parallel inhibition curves in the RIA and inhibition was produced by IgD and not by any of the other immunoglobulins. The assay had a lower limit of sensitivity of 0.01 International Unit (I.U.)/ml and modifications increased the sensitivity to 0.0008 I.U./ml. Measurable IgD levels were found in all 112 normal adult sera assayed (geometric mean 13.0 I.U./ml, arithmetic mean 30.1 I.U./ml, median 14.8 I.U./ml, range 0.10 to 202 I.U./ml, 95% of values between 0.19 and 156 I.U./ml. The distribution of IgD in the 112 normal sera appeared trimodal with modes at approximately 0.25 I.U./ml, 5 I.U./ml, and 35 I.U./ml. IgD was measurable in nasal and bronchial washes and human milk, but could not be detected in parotid fluid.

Measurement of Human Serum IgD Levels

“…Serum levels of IgD have been measured previously by a number of methods and found to vary widely between individuals. Studies of healthy individuals have reported ranges of 0.15 to 300 μg/ml (Dunnette et al, 1977) and 0.10 to 213 μg/ml (Levan-Petit et al, 2000). IgD levels follow a non-gaussian distribution, which has been reported as unimodal (Levan-Petit et al, 2000), bimodal (Litzman et al, 1997), and trimodal (Dunnette et al, 1977).…”

“…RID is much less sensitive than RIA or ELISA (sensitivity ∼1.25 to 3 μg/ml), and the method does not allow for the handling of large numbers of samples. RIA is more sensitive (Dunnette et al, 1977), but involves the use of radioactively labeled compounds, which does not allow easy handling of large numbers of samples.…”

“…Studies of healthy individuals have reported ranges of 0.15 to 300 µg/ml (Dunnette et al, ) and 0.10 to 213 µg/ml (Levan‐Petit et al, ). IgD levels follow a non‐gaussian distribution, which has been reported as unimodal (Levan‐Petit et al, ), bimodal (Litzman et al, ), and trimodal (Dunnette et al, ). Reported geometric means also vary, from 40 µg/ml to as low as 2 µg/ml (Preud'homme et al, ).…”